Why You Have Ice Formation In Mini Split AC Outdoor Unit

AC freezing can be a dangerous thing, whether inside or outside the house. It creates an increased risk of air conditioner failure and may even damage the AC.

Even if it starts outside, freezing can quickly spread to the indoor unit, causing water damage. A frozen unit may also not operate so efficiently.

So, what causes outdoor freezing in mini split air conditioners, and is there anything you can do about it? Here’s what you need to know.

Why Does Ice Collect on the Condenser Unit?

It all has to do with how the air conditioner works. Mini-split air conditioners extract air from inside the house and dump it outside. The reverse is true in winter. The heat pump extracts heat from the outside air and sends it into the house to raise indoor temperatures.

When working as an AC, warm, stale air from your home passes over the evaporator coils located within the indoor air handler uni,t where the heat is extracted and carried outside by the refrigerant material. The now-cool air then returns into the house via the return vents.

It means that the evaporator coils must be very cold. This is usually facilitated by the cycling of the refrigerant. The refrigerant leaving the condenser outside the house for the evaporator unit indoors is very cold.

However, the coils are also not supposed to freeze. Otherwise, it would block airflow and compromise the functioning of the air conditioner. This process is also facilitated by the cycling of the heat exchange between the refrigerant and indoor air. The heat extracted from indoor air helps “balance” the temperatures inside the evaporator to prevent freezing.

Now, imagine a scenario where the temperature balancing process is compromised. Specifically, imagine a situation where there’s not enough heat to keep the coils from freezing! The evaporator coils would most likely freeze up.

But it’s not just the evaporator coils that would freeze up. The refrigerant would also become extremely cold, causing the refrigerant lines to freeze. In extreme cases, the freezing can extend to the outdoor condenser.  

The Two Main Causes of Outdoor Condenser Freeze-Up

So, why would there not be enough heat to facilitate the temperature “balancing” process to keep the evaporator coils frost-free? There are two common reasons;

Restricted airflow over the evaporator coils

As we’ve seen, the air conditioner depends on warm air coming from your home to keep the evaporator coils from freezing. If there’s impeded or constricted airflow, the coils may become too cold and ultimately freeze up. Restricted airflow over the evaporator coils can result from the following;

  • Clogged air filters: Air from your home passes through a set of filters when entering the air handlers. This is an important step in the cooling process as it protects the AC from dust and other particles that may cause malfunction. However, over time, the filters can build up too much dirt, causing blockage and airflow constriction.
  • Dirty evaporator coils: Although the filters do an excellent job in most cases, a compromised filter may allow smaller dirt particles to enter the air conditioner. If these particles build up on the evaporator coils, it can reduce the surface area available for heat exchange.
  • Malfunctioned blower fan: The blower fan is tasked with drawing stale, warm air into the air conditioner and pumping cool, fresh air out of the AC and throughout the room. If the fan fails to draw in enough warm air, you may not have enough heat to keep the evaporator coils from freezing.
  • Closed or blocked air vents: Finally, you may also have unusually low airflow across the evaporator coils if the air vents are blocked. Blockage at the vents can be caused by dirt buildup or a damaged vent. Or it could be a piece of furniture blocking the vent.


The first step to addressing airflow issues in your air conditioner is to ensure proper and timely maintenance. Make sure the filter, fan, and condenser coils are clean and free from obstructions. Also, make sure that there are no leaky ducts or fan malfunction. However, if the damage has already happened, act as appropriate by changing the filter or cleaning the vents accordingly.

Low refrigerant levels

Another thing that may affect the temperature balancing inside the evaporator coils, potentially resulting in freezing inside and outside the house, is low refrigerant levels.

Refrigerant is the lifeline of any air conditioning system. It’s like blood in the human body. Lose a little bit of it, and you might enter a coma. Lose too much, and you’re staring at death.

If there’s a low level of refrigerant in your AC, the capacity to absorb heat reduces drastically, often resulting in low cooling efficiency. It also means that the refrigerant may become colder, which can cause freezing inside and outside the house. Causes of reduced refrigerant levels include;

  • Refrigerant leaks: Refrigerant can leak from the line set, the condenser, or the indoor air handler. Inside the compressor and air handler, leaks are mainly due to wear and tear (that causes holes) and poor flaring. Meanwhile, in the refrigerant lines, it often happens when the lines are bent or pierced.
  • Malfunctioned condenser: The condenser unit is solely responsible for pump refrigerant around the air conditioner. It provides the pressure that keeps the refrigerant cycling. Therefore, a malfunction can cause low refrigerant levels.


Low refrigerant issues are best handled by a licensed technician for two reasons. First, you need a license to handle refrigerants. Otherwise, you may end up in jail.

Secondly, refrigerant is dangerous for your health. It causes respiratory conditions that may cause loss of consciousness and even fainting. Shut off the AC and call a technician.

Now You Know

Air conditioner ice formation can happen to anyone. However, in most cases, it happens if there’s poor maintenance. For example, you’re at greater risk if your AC filters are clogged, the vents blocked, and the fan damaged. Regular maintenance can save you from costly damages.

More importantly, though, always know when to call the pros. For example, if you notice signs of low refrigerant, it is best to shut off the unit and call an HVAC professional.

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